This paper assesses the explanatory power of a perspective arguing that school social segregation enhances social inequalities in political engagement because of the distinct effects that concentrations of adolescents of disadvantaged backgrounds in educational settings generate. It tests this argument with data of the 2000 Civic Education Study among Upper Secondary students and uses intentions to participate and political competences as outcomes to represent political engagement. Social inequalities in political competences turn out to be greater in states with the most segregated systems, but social disparities in intentions to participate are unrelated to the level of segregation. The paper argues that policy makers should consider creating a more integrated school system if they seek to reduce social inequalities in "informed" political participation.